The present invention relates to an apparatus for locking a propeller on a marine motor and preventing theft thereof. The need exists for a device to protect the propeller on an outboard or inboard marine motor from theft. Propellers are generally secured to the motor by an exposed tab washer or cotter pin and propeller nut. The exposed nature of the nut provides for quick and easy removal of a propeller. A device which covers the exposed nut would be useful in preventing the theft of propellers.